The present invention is related generally to orthodontic-dental appliances and more particularly to retainers intended to guide post-treatment settling processes.
Conventional retainers, such as the Hawley retainer, are often used for orthodontic purposes for the maxillary anterior teeth. This retainer is comprised of a metal wire positioned across the labial surface of the maxillary teeth and an acrylic portion positioned across the lingual surface of the maxillary teeth. This retainer is normally worn for a period of eighteen to twenty-four months and is commonly worn full-time for the first six months, one-half time for the second six months, and at night for the remainder of the time period. This retainer, however, suffers from several drawbacks including physical irritations and allergic reactions to the lingual acrylic portion of the retainer. Furthermore, because the retainer is removable, it is often lost, misplaced or damaged. Additionally, for cosmetic reasons, many patients refuse to wear the retainer or wear it for only a portion of the time necessary. Thus, it is desirable to minimize the time during which a patient must wear a Hawley retainer. Finally, some adult patients suffer from a loss of alveolar bone support and a Hawley retainer alone is not adequate for retention.
Once the teeth have been properly aligned by the orthodontic appliance, it is necessary to continue wearing the Hawley retainer at least a portion of the time such that the teeth do not relapse to the prior condition. Certain extreme pretreatment maxillary deficiencies such as crowding, spacing, rotation, palatally blocked lateral incisors, and muscle imbalance, require more secure, semipermanent retention than removable maxillary retainers provide. One solution is the bonding of a passive splint wire to the lingual surfaces of the maxillary anterior teeth with a plastic substance. However, this direct bonding process is often inaccurate, tedious and time-consuming and does not yield consistently reproducible results. Another solution is the bonding of a cuspid to cuspid lingual retainer which is preformed and available in graded sizes. Preformed lingual retainers, although they provide effective retention in the mandibular arch, have not been as successful in retaining maxillary anterior teeth. This is due to the fact that the strength of the retainer and accuracy of its position in the maxillary arch is much more demanding because of the irregular tooth morphology of maxillary incisors and the greater need to withstand mechanical occlusal stress. Also, since too few size increments are available, preformed anterior retainers are frequently too long or too short to fit accurately. Maxillary retainers that do not fit precisely lack resistance form and do not effectively permit occlusal forces to be dissapated in the teeth and periodontal structures. Consequently, the shearing forces applied more readily weaken the resin bond and lead to bond failure. Thus, although desirable, bonded retention of maxillary anterior teeth has remained difficult and has not gained wide acceptance.